Cyrene- and water-based exfoliation of black phosphorus for potential nanolayer-mediated disaggregation of insulin fibrils

Liquid suspensions of phosphorene nanolayers (2D-bP) obtained through liquid phase exfoliation (LPE) of elemental black phosphorus (bP) have been prepared and extensively characterized. The exfoliating ability of deionized water (DI water), dihydrolevoglucosenone, (Cyrene), and N-methyl-2-pyrrolidone (NMP) has been investigated and compared along with the differences in the structure, concentration, and stability of the collected nanoflakes. Water was chosen as an exfoliating medium due to its harmlessness and cost-effectiveness and because it is the safest solvent for further potential biomedical applications. Cyrene is a new bio-based solvent still under study. NMP, which is among the most widely used solvents for the exfoliation of 2D systems including bP, has been employed for comparison. The obtained suspensions have been characterized by Dynamic Light Scattering (DLS), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Phosphorus 31 Nuclear Magnetic Resonance (31P NMR), Transmission Electron Microscopy (TEM), Ultraviolet -Visible (UV–Vis), and Raman spectroscopies. The stability of 2D-bP suspensions over time and their photoactivity, i.e., their ability to generate singlet oxygen species as a photosensitizer, have been investigated. The collected results evidenced that the exfoliation of bP in different solvents, including DI water, resulted in satisfactory and comparable nanoflake structures and features. The singlet oxygen generation through irradiation of 2D-bP in DI water suspensions, advantageously obtained directly from LPE, showed promising potential for use in photodynamic therapy (PDT). Preliminary data on the potential biomedical application of 2D-bP to inhibit the insulin self-assembly into amyloid aggregates as well as to cause fibrils disassembling through simple incubation or photoactivity, are also discussed.